At first glance, a $129 smoke detector sounds wildly overpriced — and it would be, if that’s all the Nest Protect was. It’s also a carbon monoxide detector. “Dumb” combination detectors can sell for $55 or $60, so you’re already half way to the Nest’s sticker price without adding in its more advanced functions.

As iFixit revealed in their teardown, it’s the additional high-tech internals (and the clever design) that you’re paying for. The Nest Protect features a Broadcomm 802.11 b/g/n Wi-Fi chip, just like many smartphones, tablets, and laptops. It’s also ZigBee compatible, so you can easily connect it to a wide range of home automation controllers.

It doesn’t take much processing power to run the Protect, as you might have guessed. Despite its high-tech connectivity and sensors, a 100Mhz Freescale chip is all that’s required.

And speaking of sensors, iFixit posted a nice photo of the Nest Protect’s dual motion sensors. One is vertical, the other slightly angled, which allows it to easily pick up frantic waving when an alarm needs to be silenced. That’s one more thing you’re paying for: the convenience of not having to drag a chair over so you can climb up and press a button to reset.

Nest even throws in a half dozen Energizer e² lithium batteries, and those don’t come cheap. They’ll also power the Protect — LED night light and all — for multiple years.

While iFixit found the Nest Protect simple enough to tear down, they’re not assigning a repairability score. Why not? Because a household smoke and CO detector isn’t really the kind of thing you generally should be taking apart — other than removing the cover to change batteries.